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Bridge mode
Introduction of Bridge mode The Bridge mode from the common user's perspective is usually be seen in the configuration page of their home routers. This function basic serves for combining 2 different routers into single LAN, instead of two LANs, i.e., connect two different routers for extending the home LAN coverage. Technology Perspective Network bridging is the action taken by network equipment to create an aggregate network from either two or more communication networks, or two or more network segments. Bridging is distinct from routing which allows the networks to communicate independently as separate networks. A network bridge is a network device that connects multiple network segments. In the OSI model bridging acts in the first two layers, below the network layer. There are different types of network-bridging technologies: simple '''bridging; '''multiport '''bridging; '''learning, or transparent '''bridging; and '''source route bridging. The bridge normally send packets between different segments of the network. The different between a bridge and a hub is a hub would repeat all the packets it received to all the ports, while the bridge would only transmit the selected packets with MAC addresses in the other side of the network segment, thus septate the Collision Domain into 2 while remain a same LAN. However, since Bridge works on the second layer, it would not be able to spilt Broadcast Domain. Then the bridge is able to translate different PHY layer, or even different protocols. The most common case is like in enterprise LAN, some of the clients, servers and devices are connected via Ethernet cables, while some of the devices like laptops or tablets are connected using wireless technologies. Having a bridge would provide a single network structure while filtered out the packets within same technology, reduce the unnecessary traffic across the different segments of the network and improve the overall throughput by this method. For Ethernet, the transparent (Learning) '''bridging was used and the bridge would connect segments of the network. Through transmitting, the bridge would learn and to record the MACs on different sides of the network and maintain a table of MACs inside of its memory. If the bridge support NM, the manager would be able to create and alter the table through SNMP. To achieve best performance, the frequent connections should in the same side of the bridge, reducing the traffic pass through the bridge, e.g. servers and databases that communicate more often and have larger traffic than other nodes. Home Routers For most cases in home routers, the bridge mode is used when a user wanted to connect 2 different home routers. Most of the common home routers being distributed in the Australia are actually integrated with modem and router, and many services are being hosted on the router, like DHCP and NAT. The issue arises when you try to connect another router behind this configuration, and end up having 2 DHCP servers and 2 NATs, creating issues for port forwarding and the like. In some cases, where the same brand products are used, the IP addresses will conflict and the devices will not connect at all when they are connected together. Then one router should then be bypassed, served as only a bridge which convey only packet through, leave other duties for the Main router. Bridge here are not kind of dedicated device mentioned above, but mainly a software function enabled on the router. This would help the home network to cover more area than a single router. Wireless Distribution System for Wi-Fi The Wireless Distribution System for Wi-Fi is a easier approach for home routers to extend the wireless coverage with minimum configuration. It enables the wireless interconnection of access points in an IEEE 802.11 network. It allows a wireless network to be expanded using multiple access points without the traditional requirement for a wired backbone to link them. The notable advantage of WDS over other solutions is it preserves the MAC addresses of client frames across links between access points. An access point can be either a main, relay, or remote base station. * A '''main base station is typically connected to the (wired) Ethernet. * A relay base station relays data between remote base stations, wireless clients, or other relay stations; to either a main, or another relay base station. * A remote base station accepts connections from wireless clients and passes them on to relay stations or to main stations. Connections between "clients" are made using MAC addresses. All base stations in a wireless distribution system must be configured to use the same radio channel, method of encryption (none, WEP, WPA or WPA2) and the same encryption keys. They may be configured to different service set identifiers. WDS also requires every base station to be configured to forward to others in the system. WDS may also be considered a repeater mode because it appears to bridge and accept wireless clients at the same time (unlike traditional bridging). However, with the repeater method, throughput is halved for all clients connected wirelessly. WDS may be incompatible between different products (even occasionally from the same vendor) since the IEEE 802.11-1999 standard does not define how to construct any such implementations or how stations interact to arrange for exchanging frames of this format. The IEEE 802.11-1999 standard merely defines the 4-address frame format that makes it possible. Using this method provide a easier approach for creating WLAN with multiple access points, while no cable backbone needed. Most of the modern home routers shipped were capable for WDS. Reference 1 ADSL Modem / router full bridge mode tutorial, Whirlpool.net.au, http://whirlpool.net.au/wiki/adsl_modem_router_bridge_mode 2 Network Bridging, Wikipedia, http://en.wikipedia.org/wiki/Bridging_(networking) 3 Internetworking Concepts, http://manipalitdubai.com/material/Lecture_Notes/ISM201/Internetworking_concept.ppt 4 Wireless distribution system, Wikipedia, http://en.wikipedia.org/wiki/Wireless_distribution_system